How much gas does your genny use? And a charging question

[Naio]

After generous advice and hand-holding from folks here, I experimented with running my van engine to charge house batteries when dry camping, as I do not yet have a genny or solar. I used an MSW inverter and a 30 amp 'smart' charger. Now I have results to post and subsequent questions.

I did this for a total of 7 days at two campgrounds. At the first cg, I felt bad because my van engine was louder than the neighboring gennys. At the second cg, I did not, because some gennys were louder than my van, so I felt I was fitting in with social norms :).

It's hard to estimate, but it seemed to take about 1/2 gallon per hour, idling the van. Seems like a lot of wasted energy. How much does a small generator use? OTOH, the van gets nice and warm for sleeping at night!

Charging this way took a LOT longer than plugging in to 120v. I don't have an ampmeter yet, but it took around 3x as long. Same charger. Is there anything I can do to speed things up? My alternator is 105v, so I don't think that is the problem.

[Almot]

Naio wrote:
At the first cg, I felt bad because my van engine was louder than the neighboring gennys. At the second cg, I did not, because some gennys were louder than my van, so I felt I was fitting in with social norms :).

For a snowbird "some" solar is very desirable. With today's prices I would say - a must. On a camper van you can probably have 200W total.

As noted, the last 10% of charge is very slow, you're running your engine or a generator with almost same noise level and substantial gas per hour, while your battery can only accept a few amps or less. Solar will do the last 10-15% quietly. On some days maybe "the last" 50%, i.e. no engine or generator use. Though this would make your fitting with "social norms" even more difficult, especially when somebody is running an open-frame contractor grade generator all day.

[MrWizard]

A 6kw Onan will use 1/4 idling and about 1/2 gallon charging my batteries, so your not that bad off
But
My 3kw Champion inverter genset, will give me about 5.5 hrs charging and other small loads on one gallon

The small $99 two stroke 900w generator will quickly pay for itself, in fuel savings, if your spending a lot of time camping

BTW your alternator might be 105 amps, but it is only 14v not 105v that would burn up every thing in the van

[pnichols]

Naio wrote:
It's hard to estimate, but it seemed to take about 1/2 gallon per hour, idling the van. Seems like a lot of wasted energy. How much does a small generator use?

The generator we use for charging the RV's battereis has a 0.51 gallon tank. It will run about 5-6 hours on this tank.

However, we do sometimes idle our main Class C's engine to charge the batteries for about the first hour to really pump in the amps before we use the generator. I've read that the main engine we have (a Ford V10) consumes about 0.7 gallons per hour when idling. The V10 idles quieter than any generator, so it provides a handy way to put a lot of charge back into the RV batteries when we want to be real stealthy in sensitive situations anywhere anytime whether the sun is shining or not.

Of course it's wasteful to use a big V8 or V10 to charge RV batteries. But it's also very practical to use what you have to accomplish something instead of buying something additional to do the same thing ... when you might have better ways to spend that money. 😉

[time2roll]

SAR Tracker wrote:
Let me get this straight....
You're running your vehicle to provide 12v to the inverter to provide 120v to a charger to provide 12v to a battery.

doesn't your vehicle charge batteries off the alternator? :h

https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/28204118/srt/pa/pging/1/page/3.cfm

[BFL13]

Works for me! I tried it out to use as Plan B if the Honda gen won't work for some reason. In this case, the OP doesn't have a Honda at all.

Idled truck for an hour no problem, the Vector charger ran normally. I had a MSW Xantrex inverter at the time, shown hanging out from the fender (it overheated and shut off when up on the fender closer to the engine)

[sushidog]

My cheapo Chinese genny burns about a gallon every 4-5 hours depending on load - but it only puts out 1,200 watts (1,500 watt surge). The Honda is much more efficient. The EU2000 Honda will run from about 4-10 hours on a gallon of gas, depending on load. What makes the Honda more efficient is the ability to reduce RPM as load decreases, as it is an inverter genny. The most efficient inverter generators is the Boily, because their electronics are more efficient. Unfortunately they only have one model, a 3,000/3,300 watt model (a little more output than a 2,800 watt/3,000 watt Honda). According to the literature it only takes .55 liters of gas to produce 1 kwh of power, while the 3,000 watt Honda burns .64 l/kwh. The Yamaha and Kipor tie for second in the efficiency dept., both burning .58 liters of gas per kwh. If efficiency were a big concern I would choose the Yamaha, sacrificing a bit of efficiency for the better reliability and dealer support vs the Boily - that is if you really need a genny this large - say to run your ac and microwave.

http://bottomlinetrading.com/BOLIYCOMPARE.html

Chip

[SAR_Tracker]

Let me get this straight....
You're running your vehicle to provide 12v to the inverter to provide 120v to a charger to provide 12v to a battery.

doesn't your vehicle charge batteries off the alternator? :h

[rv2go]

I use my Honda EU1000i late evening to bed time. 5 hours on about a quart of gas or less. I start the Honda when my house batteries get to 12.5 volts. I set the charge rate at 5amps on my Inverter/Charger. This allows the TV, 2 computers, the ice maker, and what lights that are needed to run. Fridge is on gas. By bedtime, the batteries are in the float stage. 13.2 volts.

[the_bear_II]

I once had a Honda 1000W generator that I used to re-charge two 12v batteries on my TT. It was very quiet and would run all day on about 1/2 gallon of gas.

The 1000w was enough to run lights, TV and VCR at night and then charge batteries the next day.

It worked great when boondocking.

[Dakota98]

From your posting a few weeks ago & now that you have experienced first hand, attempting to charge via the vehicle, I think the conclusion as was stated by several responses then.

In your circumstances, you need a small generator & a good smart charger when dry camping.

Any small genny uses very little gas & in the long run will suit the purpose & pay for itself with less fuel consumption.

[BFL13]

My Vector smart chargers work ok on MSW.

How did you measure that amount of recharge achieved for the comparison of times?

You would need to start from the same state of charge (SOC) and get to the same higher SOC and compare the times. It is fairly simple to get the starting SOC from a "mostly" resting voltage (nothing much 12v running at the time) it is very hard to determine the subsequent SOC as charging proceeds because now your battery voltage rises, and your hydrometer is behind the problem due to "SG lag"

If you have an amps read-out on the charger that helps a lot. My "marker" for 90% SOC when to stop the charge is when amps have tapered down to 5 amps per 110AH of bank at 14.5 volts. eg with a pair of 27s at 110AH each, that would be when amps are down to 10 amps.

Anyway, without some way to tell charging progress, how can you say it takes three times longer using that method?

[pianotuna]

Hi,

The charger doesn't "like" the wave form from the MSW inverter.

[naturist]

Running your van engine to charge the batteries is rather wasteful, both of gasoline and of engine life on the van. I've a little ECQ 1800 watt inverter generator that will run for about 5 hours on the quart of fuel in its tank. I've also got a 5500 watt open frame generator that will run for at least 12 hours on 7 gallons of fuel, a lot longer (but I don't know how long) on a light load such as a 30 amp battery charger (which, after all, claims to provide only 360 watts worth of charge to the battery). What you did is in some ways equivalent to hitching up a full-size bulldozer to pull up your tent stakes.

I'm thinking that the reason that your battery charger took so long is the MSW inverter you used to feed it. Obviously I've no knowledge of the circuitry in that charger, but I suspect that it would be much faster if feed from a pure sine wave power supply. Most battery chargers of the automotive sort use a transformer to reduce the voltage to 12 from 120, (at least the ones I've seen), and a transformer is only going to provide power during the rise/fall time of the waveform, meaning that for most of the cycle, they will yield nothing, thus being very inefficient.

I quite understand the costs involved in buying a suitable small generator. I passed through a Northern Tools store just yesterday and saw that they had a pile of 2000 watt inverter generators of their own Powerhorse brand claiming to run at only 52 dB noise level (which is quieter than Hondas, albeit not by much) for only $599.

Do be aware that for running that battery charger, even one of those tiny 900 watt, 2 cycle, $99 Harbor Freight generators is quite adequate.

[time2roll]

I find it odd the charging took 3x as long as at home. More likely the battery was lower on charge than you think. Did you monitor the charge to verify it was not shutting down intermittently? Need an ammeter to verify the charger is working same on inverter vs. utility power. Most don't charge to 100% while camped because the last 10% does take an extended period.

[dave17352]

My honda eu3000 will run twenty hours on 3.5 gallons of gas on eco mode which would be plenty to run a charger. That's weird that it took three times as long with the inverter unless of course its not supplying your inverter with enough power. In which case maybe that is not good for your charger.